PULSE OXIMETRY (SpO2) is a noninvasive tool for continuously monitoring a patient's oxygenation status by measuring the arterial oxygen saturation of hemoglobin. Because it's only an adjunct to patient assessment, pulse oximetry must be used in conjunction with other data, such as vital signs.
Applied to a peripheral site such as a finger, a pulse oximetry sensor consists of light-emitting diodes (LEDs) and a photodetector usually located directly opposite the light source. The LEDs transmit red and infrared light through the tissues to the photodetector, which captures changes in light absorption by hemoglobin. The monitor uses information from the sensor to calculate oxygen saturation in arterial blood and also measures average pulse rate.
Pulse oximetry monitoring is indicated whenever a patient is at risk for developing hypoxemia. Make sure you know the limitations of pulse oximetry. For example, SpO2 inaccuracies can occur in patients with abnormal hemoglobin, vasoconstriction, hypothermia, or cardiac dysrhythmias. In addition, remember that pulse oximetry provides no information about ventilation.
In the following photos, you'll see how to apply sensors used for pulse oximetry monitoring. You can apply a sensor to a finger, toe, forehead, nose, or earlobe, as long as perfusion is adequate. (See Choosing a sensor and a site for selection criteria.) If you're using a finger, remove any nail polish first. Some shades of polish (especially brown, blue, and green) can block light transmission, resulting in an inaccurate reading. If possible, place the sensor on an unpolished nail or use another application site.
Make sure the sensor and monitor are compatible; follow the manufacturer's recommendations. Explain the procedure to the patient and encourage her to keep the application site still during monitoring because motion can affect the accuracy of the readings.
Apply the sensor to clean, dry, nonirritated, nonedematous, and intact skin. If you're using a reusable sensor, clean it before and after each patient according to the manufacturer's recommendations.
After choosing and applying the appropriate sensor, connect the patient sensor to the pulse oximetry cable, insert the cable into the sensor port on the monitor, and plug the monitor into the wall outlet. Turn on the monitor's power switch. Minimize ambient lighting to prevent inaccurate readings. Assess the patient's apical or radial pulse and compare it with the monitor's displayed pulse rate to help make sure that the monitor is functioning properly.
Set the alarm limits according to your facility's policies and procedures. Document SpO2 readings, the site assessment, and the patient's pulse.
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